This invention relates to apparatuses for blending particulate solids and further to gravity flow type of blenders wherein the granular or particulate solids are withdrawn simultaneously from a multiplicity of levels within a heterogeneous mass of the solids at various locations about the mass and thereafter recombined. It more particularly relates to so-called single-pass type blenders.
Prior apparatuses for blending dry particulate solids are comprised of mechanical devices or gravity flow type bulk silos. The mechanical devices utilized rotating agitators, rotating shells, and mechanical or pneumatic conveyors to blend the powdered solids. These devices hve the disadvantages though of small capacities, high horse power requirements, and the fact that they are expensive to construct. The gravity flow devices are limited, however, to free-flowing granular materials and comprise basically a large container for holding a bulk quantity of material, with a plurality of tubes having inlets located around the container. The particles are drawn and flow under the force of gravity to a common blending chamber. The granuler solids can either be withdrawn from the unit or re-circulated to the top of the large container.
In the prior art, gravity blenders have a disadvantage of a start-up heel occurring when the blender is filled. The first material charged into the unit goes directly to the blending chamber and is unblended. The normal procedure in the past to correct this problem has been to discard this start-up heel of material or to re-circulate all of the material to the top of the unit for additional blending.
Blenders of the prior art are limited to materials that are free-flowing when acting under the influence of gravity. The inlet to the blending tubes extends into the blending bin typically. This presents a restriction to the flow of material. Further, the blending flow control devices of past gravity blenders were designed such that unless the material was free-flowing, it would tend to bridge in the blending chamber. Thus, past gravity blenders were unable to efficiently handle materials having sluggish flow characteristics.